1. Field of the Invention
The present invention relates to a hull parameter setting method of setting suitable hull parameters characterizing the hull of an airship that ascends and descends at high altitudes in the stratosphere through buoyancy control in conformity with the actual conditions of ambient air, a hull parameter setting system for carrying out the method, and a method of adjusting the ascension rate of the airship for which hull parameters are set.
2. Description of the Related Art
An airship that ascends and descends at high altitudes in the stratosphere through buoyancy control is a very large aerial vehicle provided with a Helium room filled with Helium gas and an air room filled with air, and having a diameter of several tens meters and a length (height) in the range of several tens to several hundreds meters. Referring to FIG. 6 showing a conventional airship 1, the airship 1 has a hull provided with a Helium room 2 and an air room 3 separated from the Helium room 2. When the pressure difference between the interior and the exterior of the hull increases as the airship 1 ascends, air is discharged through a relief valve 5 to reduce hull density. The airship 1 continues to ascend until the air contained in the air room of the hull is exhausted. As the airship 1 ascends and the air is discharged from the hull, the air and the Helium gas contained in the hull expand and the respective temperatures of the air and the Helium gas decreases accordingly. Consequently, the air and the Helium gas become unable to expand, air discharge rate at which the air is discharged from the hull decreases, and the ascension rate decreases. Thermal energy is supplied to the airship 1 by radiation from the sun and the earth and by transfer from the atmosphere to raise the respective temperatures of the air and the Helium gas contained in the hull. Consequently, the temperature of the air rises, the air expands, the air is discharged, and the airship 1 continues to ascend. Shown in FIG. 6 are an air temperature/differential pressure sensor 6 capable of measuring the temperature of the air in the hull and the pressure difference, a motor-operated Helium valve 6, a Helium temperature/pressure difference sensor 7, an atmosphere temperature/moisture sensor 8, a skin temperature sensor 9, and on-board equipment 10.
The conventional airship 1 is designed so as to be capable of ascending in the standard atmosphere having a standard atmospheric density gradient specifying an average atmospheric environment. The ascending performance of the airship 1 is greatly dependent on the rate of change of the density of the atmosphere surrounding the airship 1. Atmospheric density decreases with altitude. In the actual atmospheric environment, the reduction rate of atmospheric density is affected by land and maritime meteorological factors including seasonal factors, and geographical factors. The atmospheric density decreases at different reduction rates on different days, at different times and at different places, respectively. If the atmospheric temperature distribution has a part of discontinuity where the atmospheric temperature does not decrease monotonously with altitude, i.e., if the atmosphere has a temperature inversion layer where the atmospheric temperature rises with altitude, the reduction rate of atmospheric density increases sharply in the temperature inversion layer. Consequently, the buoyancy of the airship under buoyancy control decreases and the airship is unable to ascend past the temperature inversion layer and stays at the same altitude for some time, which extends time necessary for the airship to ascend to a desired altitude.
The occurrence of the temperature inversion layer will be described with reference to FIGS. 7A to 9B showing graphs simulating the actual conditions of the atmosphere at 9 am in May and June of 1995 at Nemuro, Hokkaido. The graphs shown in FIGS. 7A, 8A and 9A show the variation of temperature with altitude, and the graphs shown in FIGS. 7B, 8B and 9B show the relation between altitude, speed, pressure difference, and time elapsed after the airship has started ascending. As obvious from FIG. 7A, temperature decreased monotonously with altitude. The relative frequency of days where ascending time is 1 hr (3600 s) or below as shown in FIG. 7B in sixty-one days in May and June was 16.4% (ten days). None of the sixty-one days in May and June satisfied airship ascending test conditions including a surface wind velocity of 5 m/s or below and a cloud amount of 40% or below. As obvious from FIG. 8A, the temperature gradient had a discontinuous part at altitudes in the range of 1 to 2 km. The airship was caught temporarily by the temperature inversion layer during ascension, and the relative frequency of days where ascending time was in the range of 1 to 2 hr as shown in FIG. 8B in sixty-one days in May and June was 72.1% (forty-four days). As shown in FIG. 9A, the temperature gradient had a discontinuous part at altitudes in the range of 0 to 2 km. The airship stayed for some time in the temperature inversion layer during ascension, and the relative frequency of days where ascending time was not shorter than 2 hr as shown in FIG. 9B in sixty-one days in May and June was 11.5% (seven days). As apparent from those graphs, temperature inversion layers occur frequently. Therefore, the conventional method of controlling the buoyancy of an airship on the basis of the standard atmospheric conditions is unable to make the airship exercise necessary ascending performance.
The ascension rate of the airship is dependent on the general effect of the expansion/compression of the air and the Helium gas in the hull, the amount of thermal energy given to the airship by solar radiation, the rate of heat exchange between the airship and the atmosphere by convection, the rate of heat exchange between the airship and the earth, the universe and the atmosphere, air supply to and air discharge from the hull, and the aerodynamic ability of the hull. Therefore, proper hull parameters must be set, grasping those factors affecting the ascension rate. However, the airship is unable to ascend according to a proper ascension profile unless the hull parameters conform to the actual ambient air conditions immediately before starting ascension.
Accordingly, it is an object of the present invention to provide a method of setting suitable parameters of the hull of an airship such that the airship is able to ascend according to a proper ascension profile conforming to the actual conditions of ambient air, a system for carrying out the method, and a method of adjusting the ascension rate of the airship.
A first aspect of the present invention is a hull parameter setting method of setting parameters of a hull of an airship provided with a Helium room and an air room separate from said Helium room, comprising: launching observation means configured to observe upper air environment immediately before launching said airship in order to acquire ambient air data on actual conditions of upper ambient air including altitude, pressure, wind direction, wind speed and temperature; determining an ascension profile for said airship by a simulation using said ambient air data on said actual conditions of said ambient air; determining an initial quantity of a Helium gas in said Helium room of said airship conforming to said actual conditions of said ambient air; and adjusting a quantity of said Helium gas contained in said Helium room to said initial quantity of said Helium gas to set an initial buoyancy.
Preferably, the hull parameter setting method further comprises: observing changes in said upper ambient air with a meteorological observation instrument in a period between a completion of adjustment of said initial quantity of said Helium gas and a launching of said airship after acquisition of said ambient air data on said actual conditions of said ambient air using said observation means; correcting said ascension profile for said airship by a simulation using both said ambient air data on said actual conditions of said ambient air and a data on said upper ambient air obtained by observing said changes in said upper ambient air with said meteorological observation instrument; determining an initial quantity of Helium gas in said Helium room conforming to latest conditions of said upper ambient air; and adjusting said quantity of Helium gas in said Helium room to said initial quantity of Helium gas to set said initial buoyancy.
Preferably, said observation means includes a GPS sonde.
A second aspect of the present invention is a hull parameter setting system for setting hull parameters for a hull of an airship comprising: an observation system including means configured to observe upper air environment that is launched in order to obtain ambient air data on actual conditions of an upper ambient air including altitude, pressure, wind direction, wind speed and temperature; a simulator installed on a ground to determine an ascension profile for said airship by a simulation using said ambient air data on said actual conditions of said upper ambient air provided by said observation system and to determine an initial quantity of Helium gas in said Helium room conforming to said actual conditions of said upper ambient air; and a Helium gas controller installed on said ground or said hull to adjust a quantity of Helium gas in said Helium room according to said initial quantity of Helium gas determined by said simulator.
Preferably, the hull parameter setting system further comprises a meteorological observation system including a meteorological observation instrument for observing changes in said upper ambient air in a period between a completion of adjustment of said quantity of Helium gas and a launching of said airship after said acquisition of said ambient air data on said actual conditions of ambient air and sending a data on said upper ambient air obtained by said meteorological observation system to said simulator.
Preferably, said observation means includes a GPS sonde.
A third aspect of the present invention is an ascension rate adjusting method adapted to be used to adjust an ascension rate of an airship of which hull parameters are set by said hull parameter setting method, wherein said ascension rate at which said airship ascends is adjusted according to changes in actual conditions of ambient air by adjusting a number of air relief valves to be operated among a plurality of air relief valves of said airship or adjusting characteristics of said air relief valves to adjust air discharge rate.
Preferably, said observation means includes a GPS sonde.
A fourth aspect of the present invention is an ascension rate adjusting method adapted to be used to adjust an ascension rate of an airship of which hull parameters have been set by said hull parameter setting method, wherein said airship is loaded with a ballast if said airship has a spare takeoff weight, and said ballast is thrown out when said ascension rate of said airship decreases during ascension to increase a buoyancy of said airship and to increase an ascending ability of said airship.
Preferably, said ballast includes water.
Preferably, said observation means includes a GPS sonde.